1. Field of the Invention
The present invention relates to planar light emitting waveguides such planar plate or slab waveguides distributing light along the broad surface of the plate and emitting the distributed light from the broad-area plate surface. This invention also relates to an apparatus and method of inputting light into a planar waveguide through its face as opposed to edge-lit light guide panels where light is input through one of the waveguide edges. More particularly, this invention relates to panel luminaires, illuminated panel signs, illuminated window pane signs, front lights, backlights, lighting panels, LCD display backlights, computer screens, advertising displays, road signs, and the like, as well as to a method for redistributing light from a variety of light sources.
2. Description of Background Art
Conventionally, light emitting devices employing a planar waveguide include an optically transmissive plate, a light source coupled to the plate's edge and a series of optical features distributed along a major surface of the plate for extracting light at predetermined locations of the surface.
However, a number of applications exist where edges of the waveguide are not accessible or it is otherwise impractical to input light through an edge. Furthermore, many existing structural or artistic articles which can provide light guiding and distribution functions are not always readily transformable to edge-lit applications. Typical examples include framed glass windows of building facades and doors, storefront window panes, as well as various interior and exterior architectural features employing transparent glass or plastic panels.
Other examples of common objects which could be used as planar waveguides but may not be suitable for light input from an edge include but are not limited to planar slabs of glass or transparent plastic which edges are roughened or sanded. In a yet further example, the edges of some transparent slabs or panels may be tapered making it difficult to input light from a relatively large source. The light input aperture of edges may also be too small compared to the size of the light source due to the insufficient thickness of the transparent slab or panel.
It is therefore an object of this invention to provide an improved illumination system providing an efficient light input through a face of a planar waveguide as opposed to light input through an edge. It is another object of this invention to provide a convenient light injection into a planar waveguide, such as an existing window pane of a building, through its face, without having to penetrate into the waveguide's surface. It is yet another object of this invention to provide convenient light input in one area of a major surface of a planar waveguide and light extraction from the waveguide in another area of the surface. It is yet another object of this invention to provide an improved method of coupling light to a planar waveguide without having to access its edges and while substantially reducing or eliminating the unwanted light spillage due to the coupling. Other objects and advantages of this invention will be apparent to those skilled in the art from the following disclosure.